In the technical field of electron emitting material, various ones have been proposed. The tendency thereof is to demand such materials each having a higher voltage endurance and a larger electric-current density. Examples thereof include carbon nanotubes having been recently noticed, and it is required to make an endeavor to enhance an electron emission property and to increase an electric-current density for designs of electron emitting materials based on carbon nanotubes. It has been thus attempted to treat carbon nanotubes in such a manner to grow thin-films thereof in a patterned form, or to form carbon nanotubes into shapes suitable for electron emission by utilizing a print transcription technique.
However, carbon nanotubes have not been well established in production methods themselves, and still less, investigations of processing techniques therefor have been just started, thereby exhibiting an extremely difficult situation for the production methods. Further, even by conducting such laborious and difficult processing, the obtained performance is merely limited to an electric-current density in an order of several mA/cm2 at a maximum.
This leads to a limitation of usable electric field strength of an applicable material, and exceeding the limitation causes degradation and peeling off of the material, thereby causing the material to fail to withstand usage at a higher voltage and over a long time. On the other hand, such field electron emission techniques are expected to be made more active from now on, and there have been thus sought for materials each having a higher withstand electric field strength, being capable of stably emitting electrons at a larger electric-current density for a long time usage, and enabling stable and higher field electron emission, without degradation and damage of each material.
The present inventors have conducted investigations, in order to satisfy the demands. Namely, the present inventors have noticed boron nitride having been used as heat-resistant and wear-resistant materials and recently noticed as novel creative ones, have earnestly conducted investigations so as to design electron emitting materials based on such boron nitride materials, and finally have found out that those of boron nitride materials which are fabricated under specific conditions include ones each having an excellent field electron emission property and exhibiting an acute-ended shape, with a higher withstand electric field strength.
Namely, the present inventors have confirmed and appreciated: that, in case of generation and deposition of boron nitride onto a substrate by a reaction from a vapor phase, irradiation of ultraviolet light having higher energies toward the substrate leads to formation of boron nitride in a film shape and leads to generation and growth of sp3 bonded boron nitride crystals exhibiting acute-ended shapes on the film surface, where the boron nitride crystals grow in a self-organizing manner toward the light direction at appropriate intervals; and that the thus obtained film easily emits electrons upon application of electric field thereto, and the film acts as an extremely excellent electron emitting material capable of maintaining an extremely stable state and performance without degradation, damage, and dropout of material while maintaining a higher electric-current density which may be unprecedented over these kinds of materials up to now; so that the present inventors have filed patent applications (see Patent Documents 1 and 2) as a result thereof.
Patent Document 1: Japanese Patent Application Laid-Open Publication No. 2004-35301
Patent Document 2: Japanese Patent Application No. 2003-209489
Thereafter, the present inventors have further conducted investigations based on the inventions according to the previous patent applications, and have succeeded in developing a cold cathode type emitter having an excellent electron emission property and capable of emitting electrons even in the atmospheric air, and a light emission/display device utilizing the emitter, so that the present inventors also have recently filed patent applications (see Patent Documents 3 and 4) as a result thereof.
Patent Document 3: Japanese Patent Application No. 2004-361146
Patent Document 4: Japanese Patent Application No. 2004-361150
The inventions according to the previous patent applications noted just above relate to elements for emitting electrons and utilization thereof, and have focused on provision of an sp3 bonded boron nitride crystal in an acute-ended shape contributing to an electron emission property with reproducibility, so that importance has been exclusively given to an optimum reaction condition and an optimum region setting for such provision. However, it has gradually become apparent: that excellent electron emission properties are not sufficiently attained only by simple provision of specific shapes in design of emitter; and that extreme importance is to be given to an in-plane distribution density of acute-ended crystals. Namely, it has become apparent that excessively higher or excessively lower crystal distribution densities rather lead to deteriorated electron emission properties, respectively. Excessively higher densities problematically cause electric fields to fail to sufficiently permeate into the vicinity of crystals which are to emit electrons such that sufficient enhancement of electric fields are not realized near the acute ends, thereby leading to higher threshold electric fields for electron emission. Contrary, it has gradually become apparent that excessively lower densities problematically fail to allow larger electric currents themselves.